Infectious mononucleosis is caused by the Epstein-Barr virus (EBV), a member of the herpes virus group. The disease occurs in persons with no prior EBV antibodies. EBV-specific antibodies can be demonstrated early after onset. Antibody titers decline during convalescence, but remain detectable for life, correlating with immunity to the disease. The virus is regularly present in the oropharyngeal secretions of patients with infectious mononucleosis and often persists for months after acute disease. As with other herpes-group viruses, a persistent carrier state follows primary EBV infection.
The disease is spread through close contact, mainly by oral secretions. In areas of poor sanitation and hygiene, primary EBV infections usually occur in infancy and are silent or too mild to be diagnosed. In higher socioeconomic groups, primary exposure to EBV is often delayed until adolescence or later, when infections usually lead to typical infectious mononucleosis.
The fact the EBV transforms lymphocytes into rapidly dividing cells indicates that it may be oncogenic. There is strong evidence that EBV is involved in the etiology of Burkitt's lymphoma and nasopharyngeal carcinoma.
EBV has two high molecular weight glycoproteins on its surface (gp 350/300 and gp 220/200) and smaller amounts of other glycoproteins including a gp 85. Monoclonal antibodies and polyclonal antibodies to the gp 350/300 and gp 220/200 proteins neutralize virus infectivity.
Monoclonal antibodies frequently react with both gp 350 and gp 220. These two proteins are known to have common peptide substituents. Immunization of primates with gp 350 and gp 220 prevents infection on challenge with virus. There is also published evidence that these proteins are responsible for the specific adsorption of Epstein-Barr virus to the surface of immunoglobulin producing lymphocytes.